The present invention relates to a method of producing an encased honeycomb body.
Honeycomb bodies, which are produced by stacking and/or winding layers of sheet metal, of which at least some are structured layers of sheet metal, are known in a wide variety of forms. Honeycomb bodies including metal sheets are used as so-called support structures for catalytically acting coatings. Support structures of this type, with a catalytically acting coating, are used in motor-vehicle exhaust systems, thereby reducing the emission of certain components of the exhaust gas. Different forms of a configuration as a catalyst support structure are described, for example, in Published European Patent Application EP-A1-0 245 738.
The stacked and/or wound layers of sheet metal are at least partially soldered to one another, so that the honeycomb body is a monolithic structure. The honeycomb body is also soldered to the tubular jacket in which the honeycomb body is located. Soldering of the layers of sheet metal to one another and to the tubular jacket preferably takes place in one soldering operation. Methods of soldering a metallic configuration, including a honeycomb body and a tubular jacket, are known for example from International Publication Nos. WO89/11938, WO94/06594, WO93/25339 and from Published, Non-Prosecuted German Patent Application DE-A-29 24 592.
It is known from the prior art that the honeycomb body is provided at least partially with a bonding agent, to which a soldering powder adheres. The methods known from the prior art differ from one another with respect to the sequence of applying a soldering powder bonding agent, namely during or after the forming of the honeycomb body. A detailed account of the prior art in this respect is includes in International Publication No. WO89/11938.
The various ways of conducting the method with respect to the soldering of a configuration have various advantages. However, for the cost-effective production of a configuration it is desired to obtain a soldering method in which on the one hand a solder is introduced only into the regions in which a soldered connection is to be created, on the other hand the soldering operation is to take place as quickly as possible and with relatively little effort.
If the configuration including a honeycomb body provided in a tubular jacket is used as a catalyst support structure in an exhaust system, this configuration is subjected to thermal loading or stress. The honeycomb body and the tubular jacket have different thermal expansion characteristics on account of their different material properties. It is therefore desirable to avoid a rigid connection between the honeycomb body and the tubular jacket at at least an end region of the honeycomb body. If there are no rigid connections to the tubular jacket in the respective end regions of the honeycomb body, thermal stresses between the tubular jacket and the honeycomb body are avoided.
It is already known from International Publication No. WO96/26805 that thermal stresses can be avoided by a suitable soldering of the honeycomb body to the tubular jacket. According to International Publication No. WO96/26805, it is proposed that at least one layer of sheet metal of the honeycomb body has at least one smooth portion extending from a least one end face over part of the axial length of the honeycomb body and at least partially surrounding the honeycomb body. The smooth portion forms at the periphery of the honeycomb body an outer layer which bears against the tubular jacket. This achieves the effect that, irrespective of the soldering method, no solder gets between the outer layer and the tubular jacket. The solder can therefore be applied in the way known from the prior art. The connection of the honeycomb body to the tubular jacket takes place over part of the axial length of the tubular jacket, the smooth portion extending in the axial direction of the honeycomb body only up to the connecting region between the honeycomb body and the tubular jacket.
On account of production tolerances of the tubular jacket and the honeycomb body, however, it cannot be ensured that no solder will get between the smooth layer and the tubular jacket. To avoid the outer layers of the honeycomb body becoming connected to the tubular jacket, it is already known that the honeycomb body can be soldered through corresponding masks which cover the outer region of the honeycomb body. As a result, a connection of the outer region of the sheet-metal layers to the tubular jacket is avoided. In particular in the case of honeycomb bodies wound in an S-shaped manner, such unconnected outer regions of the layers of sheet metal cause these end regions of the layers of sheet metal to be prone to oscillate during the operation of the catalyst support structure in an exhaust system. The oscillations of the end regions may cause a destruction of the catalytically effective coating of the metallic honeycomb body.
It is accordingly an object of the invention to provide a method of producing an encased honeycomb body, in particular a catalyst support structure, which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of producing an encased honeycomb body, which includes the steps of:
forming a honeycomb body by stacking and/or winding layers of sheet metal and providing at least some of the layers of sheet metal as structured layers of sheet metal such that the honeycomb body is formed with channels for a fluid to flow therethrough;
introducing a sleeve into a tubular jacket and providing the sleeve with an axial extent of less than an axial length of the honeycomb body and of the tubular jacket and providing the sleeve with an outer circumferential surface essentially bearing against a part of an inside wall of the tubular jacket;
introducing the honeycomb body into the tubular jacket and into the sleeve; and
forming a connection between the honeycomb body and the tubular jacket and a further connection between the honeycomb body and the sleeve.
In other words, the method according to the invention of producing an encased honeycomb body includes forming a honeycomb body by stacking and/or winding layers of sheet metal, of which at least some are structured layers of sheet metal, so that the honeycomb body has channels through which a fluid can flow. At least one sleeve, which forms a bushing-shaped spacer, is introduced into a provided tubular jacket. The axial extent of the sleeve is less than the axial length of the honeycomb body and of the tubular jacket; the sleeve is preferably introduced in the region of one end face of the tubular jacket. The honeycomb body is introduced into the tubular jacket prepared in this way. The honeycomb body overlaps the tubular jacket and the sleeve. This is followed by forming a connection between the honeycomb body, the tubular jacket and the sleeve, so that the honeycomb body is connected to the tubular jacket and the sleeve. If appropriate, a connection is also formed between the tubular jacket and the sleeve. The sleeve prevents the end regions of the honeycomb body from being connected directly to the tubular jacket. The fact that the honeycomb body is connected to the sleeve achieves the effect that the sleeve forms a compensating element, compensating for the different thermal expansions of the tubular jacket and honeycomb body, and a rigid connection with the tubular jacket is not created in the at least one end region of the honeycomb body.
For technical production-related reasons, a tubular jacket has a certain circularity error with regard to it roundness. There are also tolerances with regard to the variations of an inside diameter of the jacket. As a result of this, a gap may form between the inside wall of the tubular jacket and the sleeve. To avoid solder getting into this gap, and thus creating a rigid connection between the sleeve and the tubular jacket, according to an advantageous mode of the method according to the invention it is proposed that the sleeve is pressed against the inside wall of the tubular jacket. This compensates for possible production tolerances of the tubular jacket and/or the sleeve. The pressing operation causes the spacer to undergo an expansion, if the sleeve is of an essentially tubular configuration, so that the sleeve hugs the inside wall of the tubular jacket. Consequently, between the sleeve and the inside wall of the tubular jacket there is no gap, which may cause problems and into which solder can get.
The sleeve may be of a one-piece configuration. The sleeve is preferably of a bushing-shaped configuration, so that the sleeve extends over the entire periphery or circumference of the inside wall of the tubular jacket. The sleeve may also be divided. If the sleeve is divided, the end portions of the sleeve preferably overlap, wherein the pressing of the sleeve in the radial direction against the inside wall of the tubular jacket also ensures that no solder can get between the sleeve and the tubular jacket in the overlapping end portions of the sleeve either.
Pressing of the sleeve may be so intense that the sleeve is undetachably connected to the tubular jacket. This has the advantage that the tubular jacket is easier to handle with the spacer, since the spacer cannot fall out of the tubular jacket.
According to a further advantageous mode of the method according to the invention, it is proposed that a pressing of the sleeve against the inside wall of the tubular jacket preferably takes place through the use of a mechanical pressing unit. The pressing unit preferably has a mandrel, for example an expanding mandrel, which can be introduced into the tubular jacket in which the sleeve has already been positioned. The sleeve is pressed by the mandrel against the inside wall of the tubular jacket.
Instead of an expanding mandrel, the pressing unit may apply the necessary force or the necessary pressure for pressing the sleeve against the inside wall of the tubular jacket, wherein the pressing unit has at least two radially movable segments, by which the sleeve is pressed against the inside wall. The segments may be moved radially outward through the use of a suitable ram. The advantage of this way of conducting the method is that a pressing unit for tubular jackets of different diameters can be used.
According to a further advantageous mode of the method according to the invention, it is proposed that a pressure unit is introduced into the tubular jacket and a pressure medium is directed through the pressure unit essentially radially outward against the sleeve. The sleeve is pressed against the inside wall by the pressure medium. The advantage is that the sleeve is subjected to pressure over essentially its full surface area, so that it is pressed against the inside wall of the tubular jacket.
To avoid losses of the pressure medium, according to a further advantageous mode of the invention, it is proposed that two peripheral seals are brought to bear against the sleeve. The seals are provided spaced apart from each other. The distance between the seals corresponds at most to a width of the sleeve. The seals are preferably 0-ring seals. Between the seals, at least one outlet opening for the pressure medium is provided.
The tubular jacket is preferably subjected to internal pressure through the use of a gas, with the sleeve provided in the tubular jacket. The gas is preferably air.
According to yet a further advantageous mode of the invention, it is proposed that the pressure medium is a liquid, in particular water.
By a suitable monitoring of the internal pressure or the pressure of the pressure medium, it can also be checked whether the tubular jacket is impermeable, ice. without leaks.
The pressing of the sleeve against the inside wall of the tubular jacket also achieves the effect of calibrating the diameter of the tubular jacket. This also has the advantage that possible production tolerances of the tubular jacket are eliminated, so that the tubular jacket can be connected more easily to neighboring components of an exhaust system.
According to a further advantageous mode of the invention, it is proposed that the sleeve is connected to the tubular jacket. The forming of a connection between the sleeve and the tubular jacket has the advantage that, when the honeycomb body is introduced into the tubular jacket and into the sleeve, the latter retains a predetermined position within the tubular jacket, even though the honeycomb body is pressed in the axial direction of the tubular jacket, and consequently also of the sleeve, and, as a result, exerts a force on the sleeve in the direction in which the honeycomb body is introduced.
The sleeve is preferably connected to the tubular jacket through the use of a material. A welded connection is preferred in this case. The sleeve may be connected to the tubular jacket in a punctiform manner by welding spots. Individual, essentially peripheral weld seams may also be formed.
In order to fix the sleeve within the tubular jacket, it is proposed that the spacer is connected to the tubular jacket through the use of a bonding agent or an adhesive agent. The bonding agent may be introduced in certain portions between the sleeve and the tubular jacket. The bonding agent is preferably introduced over the entire periphery of the sleeve. The bonding agent is preferably an adhesive or oil. The fact that the sleeve is pressed against the inside wall of the tubular jacket means that adhesives which only achieve their adhesiveness under increased pressure can also be used.
Alternatively or additionally, the sleeve may be adhesively bonded to the tubular jacket. The connection between the sleeve and the tubular jacket is preferably configured in such a way that the strength of the connection is less than the strength of a connection between the sleeve and the honeycomb body. In particular in the case of an adhesive connection between the sleeve and the tubular jacket, it may be possible for this connection to be released, for example, during a soldering process due to the temperatures prevailing in the soldering process.
The fact that the connection between the sleeve and the tubular jacket has a lower strength than the connection between the sleeve and the honeycomb body also ensures that thermal stresses between the tubular jacket and the honeycomb body are not introduced into the honeycomb body via the sleeve.
The sleeve is preferably produced from the same material as the honeycomb body or the tubular jacket. The connection between the sleeve and the tubular jacket is essentially an assembly connection, by which it is intended to ensure that the sleeve does not change its position within the tubular jacket during assembly, i.e. while the honeycomb body is being introduced into the tubular jacket.
The sleeve may be soldered, in particular hard-soldered, to the tubular jacket. In order to solder an axial subregion or partial region of the tubular jacket to the sleeve, soldering portions or soldering regions may be provided, which do not necessarily extend around the full periphery or circumference between the sleeve and the tubular jacket.
The connection of the individual layers of sheet metal of the honeycomb body to one another and the connection of the honeycomb body to the tubular jacket preferably takes place by one soldering operation. For soldering the configuration formed by the honeycomb body and the tubular jacket, according to a further advantageous mode of the invention, it is proposed that firstly at least one end face of the honeycomb body is brought into contact with a roller which contains a bonding agent and can be rotated about a roller axis.
The honeycomb body and the roller are moved in relation to each other in such a way that the roller rolls on at least a part of the end face of the honeycomb body and discharges or releases a bonding agent onto the honeycomb body during the rolling operation. After that, a solder is introduced at least into the honeycomb body.
This advantageous mode of the invention achieves a uniform application of a bonding agent to or into the honeycomb body. A possible unevennesses in the end face of the honeycomb body, attributable to an offset between layers of sheet metal of the honeycomb body, do not adversely affect the application of the bonding agent. The fact that the roller rolls on the end face means that wearing of the roller is also reduced, since it is not always the same locations of the roller that come into contact with the relatively thin edges of the layers of sheet metal. As a result, the service life of a device suitable for carrying out the method is also prolonged.
For applying the bonding agent, the honeycomb body and the roller may be moved. As a result, rapid application of a bonding agent is achieved if the roller and the honeycomb body are moved in a translational manner in opposed directions. To simplify the method, it is proposed that either the honeycomb body or the roller is positioned such that it is fixed in place and the roller or the honeycomb body is moved.
In the case of a honeycomb body which has at least one end region which protrudes from the tubular jacket and is of a rotationally symmetrical form with respect to a longitudinal axis of the honeycomb body, it is proposed that the honeycomb body is turned about its longitudinal axis and the roller, which has a shape adapted to the end region and extends radially inward only as far as the longitudinal axis, is turned about a roller axis intersecting the longitudinal axis at an angle of about 90xc2x0. By conducting the method in this way, the roller is brought into contact with the surface of the protruding end region.
A honeycomb body may be repeatedly brought into contact with the roller by its end face. Before a renewed contacting with the roller, it is expedient to pivot the honeycomb body by a prescribed angle about the longitudinal axis. As a result, the roller passes repeatedly over the end face of the honeycomb body, so that a very uniform application of a bonding agent is achieved.
For certain applications, it is not necessary for all the layers of sheet metal of the honeycomb body to be provided with a bonding agent. To apply a bonding agent to the end face of the honeycomb body only in certain regions, it is proposed that the roller has the bonding agent only in certain regions. This may be achieved, for example, by a corresponding shaping of the roller. By performing the method in this way, it is not necessary, for example, to interpose gluing masks.
According to yet a further advantageous mode of the invention, it is proposed that the honeycomb body is provided essentially vertically and the roller is brought into contact with an upper end face of the honeycomb body. The relative movement between the honeycomb body and the roller achieves the effect that the bonding agent does not drip into the honeycomb body.
In particular when low-viscosity bonding agents are used, it is expedient to provide the honeycomb body essentially vertically and to bring the roller into contact with a lower end face of the honeycomb body, thus dripping of the bonding agent into the honeycomb body is avoided.
According to yet a further advantageous mode of the invention, it is proposed that a honeycomb body which has two opposite end faces is brought between two spaced-apart, rotatably mounted rollers, so that the two end faces are wetted with a bonding agent essentially simultaneously.
A configuration which includes a honeycomb body provided in a tubular jacket may also be configured in such a way that the tubular jacket protrudes over the honeycomb body at least in an outer portion. In other words, the honeycomb body is provided in the tubular jacket in such a way that at least one end face of the honeycomb body is at a distance from the neighboring end face of the tubular jacket.
Such protruding outer portions of the tubular jacket form connecting regions, so that the configuration can be connected to further components or elements. For example, when using such a configuration in an exhaust system, on the one connecting region of the tubular jacket there may be provided a diffuser, which is connected for example to an exhaust pipe of an exhaust system of an internal combustion engine. It is also known for the tubular jacket to have two connecting regions, which are formed at the respective end of the tubular jacket, with essentially no honeycomb body provided in these connecting regions.
If, for example, the method of connecting the honeycomb body to the tubular jacket known from Published, Non-Prosecuted German Patent Application DE-29 24 592 A1 is used, in which the honeycomb body with the tubular jacket is dipped into a dipping bath containing a bonding liquid and is subsequently provided with powdered solder, the connecting regions of the tubular jacket are also soldered, without this being necessary or desired. The connecting regions are provided with the bonding agent not only on an inner surface of the tubular jacket but also on an outer surface of the tubular jacket. This is undesired, since it causes entrainment of the bonding agent. In particular, the handling devices which engage an outer surface of the tubular jacket are also brought into contact with the bonding agent. A considerable cleaning effort may be necessary for the handling device.
The further methods described in Published, Non-Prosecuted German Patent Application DE-29 24 592 A1 are in principle suitable for achieving a soldering of a tubular jacket and a honeycomb body, but these soldering methods are relatively complicated.
For soldering a honeycomb body in a tubular jacket, in a further advantageous mode of the invention, it is proposed that firstly a honeycomb body is formed by stacking and/or winding layers of sheet metal, of which at least some are structured layers of sheet metal, in such a way that the honeycomb body has channels through which a fluid can flow. The honeycomb body is introduced partially into the tubular jacket. The portion of the honeycomb body protruding from the tubular jacket is brought into contact by its end face with the roller containing a bonding agent. After that, the honeycomb body is introduced into the tubular jacket and a solder is introduced into the honeycomb body.
The fact that only the portion of the honeycomb body protruding from the tubular jacket is brought into contact with a bonding agent avoids the tubular jacket also coming into contact with the bonding agent. This achieves the effect that the tubular jacket is free of bonding agent, such that the soldering powder does not adhere to the tubular jacket.
Since the tubular jacket is not provided with a bonding agent, it is also not necessary to free this tubular jacket of any bonding agent in order to avoid entrainment of the bonding agent.
The fact that the portion protruding from the tubular jacket is brought into contact with a bonding agent, such that the honeycomb body is provided with the bonding agent at least partially in its axial direction, also achieves the effect that the honeycomb body is provided with the bonding agent over its entire cross-sectional area, so that even outer regions of the honeycomb body can be satisfactorily provided with a soldering powder. This ensures that a reliable soldered connection can be formed even in the outer region of the honeycomb body or between the honeycomb body and the sleeve.
According to yet a further advantageous mode of the invention, it is proposed that, before introducing the solder, a portion of the honeycomb body lying opposite therefore mentioned portion is brought into contact with a bonding agent. In particular in the case of a configuration which has a tubular jacket, the tubular jacket having a connecting region respectively at the opposite end portions, it is proposed that the honeycomb body is pushed through the tubular jacket, so that a portion protrudes from the tubular jacket. This portion is brought into contact with the bonding agent. After that, the honeycomb body is introduced into the tubular jacket in such a way that the honeycomb body essentially does not lie in the connecting regions of the tubular jacket.
For stable handling of the configuration, it is proposed that the honeycomb body is introduced into the tubular jacket in such a way that it is located in the tubular jacket over a significant part of its axial length while one or the other portion is being brought into contact with the bonding agent. As a result, the configuration has a favorably located center of gravity, which prevents tipping over of the configuration.
In particular, it is proposed that the honeycomb body is introduced into the tubular jacket in such a way that it protrudes at least 1 mm, preferably 5 mm, from the tubular jacket. This extent is adequate to prevent the tubular jacket from also coming into contact with the bonding agent.
According to a further advantageous mode of the invention, it is proposed that the portion to be wetted with a bonding agent is brought into contact with an application device which contains the bonding agent, the application device having a wetting surface which is larger than an end face of the portion and completely overlaps the latter. This advantageous mode of the invention achieves the effect that the portion of the honeycomb body can be brought into contact with a bonding agent over its entire cross-sectional area. The advantage of this way of conducting the method can also be seen in the fact that the same application device can be used for wetting honeycomb bodies which have different cross-sectional areas. It is therefore not necessary to adapt the application device to different cross-sectional geometries of honeycomb bodies.
The configuration is advantageously brought into contact with the bonding agent in a vertical position, i.e. the longitudinal axis of the honeycomb body runs essentially vertically. The application device may be provided underneath the honeycomb body for contacting the portion of the honeycomb body. A way of performing the method in which the application device is provided above the tubular jacket and the portion is brought into contact with the application device is preferred.
In the case of such a configuration of the application device, the bonding agent also flows into the portion on account of gravity. Depending on the time during which the portion is in contact with the application device and/or the dwell time of the honeycomb body in this vertical position, the effect can also be achieved that the bonding agent is introduced into the honeycomb body over the entire axial length of the latter or over part of the axial length of the latter. In order to provide the honeycomb body with a bonding agent in regions relevant for a soldered connection over its entire axial length, it is not necessary for it to spend a correspondingly long time at the application device. It is adequate if the portion remains in contact with the application device, in particular with the bonding agent, for as long as it takes for an adequate amount of bonding agent to get into the individual channels of the honeycomb body, so that adequate wetting with the bonding agent of the regions relevant for the formation of a soldered connection takes place. By conducting the method in this way, it is also no longer necessary to bring the honeycomb body into contact with a bonding agent on both sides. In particular, the time which is necessary for transporting the configuration from a wetting station, in which the bonding agent is introduced into the honeycomb body, to a soldering station, in which a soldering powder is introduced into the honeycomb body, can be used for the bonding agent to be transported of its own accord within the honeycomb body if the latter is transported in its vertical position.
In particular in the case of applying a bonding agent through the use of an application device provided above the honeycomb body, it is expedient if the bonding agent carrier or bonding agent support is of an essentially elastic and absorbent form. If, for example, the portion is pressed against the bonding agent carrier which contains the bonding agent, this achieves the effect that the bonding agent emerges from the bonding agent carrier and enters the portion. It is also possible to press the bonding agent carrier against the portion of the honeycomb body. Alternatively, the configuration and the bonding agent carrier may be moved in relation to each other in such a way that they press against each other.
In a serial soldering of honeycomb bodies, the individual honeycomb bodies are successively brought into contact with the bonding agent carrier. If these honeycomb bodies are pressed against the bonding agent carrier, there is the risk of the bonding agent carrier undergoing a loss of structure on account of material fatigue effects, which may have the result that adequate introduction of a bonding agent into the portion does not occur. This may have the effect that adequate bonding agent to which a soldering powder adheres is not made available. In order to ensure that adequate bonding agent can be introduced into the portion of the honeycomb body, it is proposed that contact surfaces of at least two successive configurations that are created during contact of a portion with-the bonding agent carrier or with the bonding agent only partially overlap. This mode of the invention is based on the consideration that the bonding agent carrier is not contacted at the same locations by successive configurations, whereby the bonding agent carrier is at least partially not stressed at the same locations, so that material fatigue of the bonding agent carrier cannot occur, or only after a much longer time.
In order to solder the honeycomb body in an axial subregion or partial region of the tubular jacket and with the bushing-shaped element, it is proposed that at least one soldering region which overlaps the tubular jacket and the element is formed. This is preferably a soldering region that is closed with respect to the peripheral direction of the tubular jacket.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of producing an encased honeycomb body, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.